Conveyor lines are often used to convey articles in facilities such as an assembly line of products and a delivery center. In a delivery center, for example, a number of conveyor lines are arranged in matrix with transfer devices disposed at positions where the conveyor lines intersect. Operations of the transfer devices transfer articles from a conveyor line to another conveyor line, so that the articles are conveyed to a desired destination.
Generally, such a transfer device includes a conveyor part for conveying articles in a longitudinal direction, another conveyor part for conveying articles in a transverse direction, and a lifting part. Normally, a top face of a conveyor part unrelated to conveyance in the longitudinal direction or in the transverse direction of the transfer device is kept below a conveying surface of the conveyor line so as to get out of the way of conveyance of the article conveyed on the conveyor line. When an article moving on the conveyor line is determined to head for a predetermined destination by a sensor or the like, the article is stopped on the transfer device by a stopper. Then, a top face of a conveyor part related to the conveyance is lifted above the conveying surface of the conveyor line by an operation of the lifting part, thereby lifting up the article. Thereafter, the conveyor part is operated so as to transfer the article to another conveyor. Such a transfer device is disclosed in Patent Document 1.